1. Technical Field
The present invention relates to an image processing apparatus and method display a myocardial perfusion image.
2. Description of Related Art
Magnetic Resonance Imaging (MRI) is an imaging method which excites nuclear spins of an object set in a static magnetic field with a radio frequency (RF) signal having the Larmor frequency magnetically and reconstructs an image based on a nuclear magnetic resonance (NMR) signal generated due to the excitation.
In the diagnosis of ischemic heart disease, as a method for evaluating myocardial blood flow perfusion by means of MRI, a method is known in which multi-slice dynamic longitudinal relaxation (T1) weighted imaging is performed for obtaining a left ventricular short axis image during the first circulation in synchronized with an ECG (electrocardiogram) after a contrast medium is injected into a vein and enhancing process of the myocardium is observed (myocardial perfusion) (see, for example, Japanese Patent Application (Laid-Open) No. 2006-87626). With regard to the images thus acquired, each of the left ventricular short axis tomographic images is divided into multiple radial regions. Then, the images thus divided are converted into development images in which the regions thus divided are concentrically arranged from the cardiac base part toward the apex cordis part, following which the development images thus converted are displayed.
FIG. 1 is a diagram showing MR images of respective sections acquired at respective dynamic time phases by a conventional myocardial perfusion imaging.
FIG. 1 shows an example of MR images 1-1, 2-1, 3-1, 1-2, 2-2, 3-2, . . . , 1-30, 2-30, and 3-30, acquired by myocardial perfusion imaging. In this example, the number of slices is a total of three sections consisting of slices 1, 2, and 3 from the apex cordis part toward the cardiac base part, and the number of dynamic time phases is 30.
Then, the myocardiums on the MR images are divided into multiple sub-regions radially, and a dynamic curve is created based upon the average image value in each sub-region. The dynamic curve is a graph representing the image value changing over time. For example, a dynamic curve A is created for the sub-region A. Further, a dynamic curve B is created for the sub-region B.
FIG. 2 shows conventional developments indicating myocardial blood flow information generated based on dynamic curves in respective small regions shown in FIG. 1. The innermost ring represents a lower cross-section of an entire ventricular wall width (divided circumferentially into eight sections). The middle ring represents an intermediate cross-section of an entire ventricular wall width (divided circumferentially into eight sections). The outermost ring represents an upper cross-section of an entire ventricular wall width (divided circumferentially into 8 sections).
As shown in FIG. 2, a dynamic curve is created for each small region with the vertical axis representing the image signal value, and the horizontal axis representing time. Specifically, FIG. 2 shows the dynamic curves A and B that correspond to the small regions A and B shown in FIG. 1, respectively. Furthermore, various parameters are calculated based upon the dynamic curves A, B, . . . and development images are created with colors or a gray scale associated with the parameter values thus calculated. For example, in FIG. 2, the maximum values of the image signals and the times till the maximum gradients of the dynamic curves are calculated as the parameters, and the parameters thus calculated are displayed in the development image 1 and the development image 2, respectively. Such a development image is called a bull's-eye. In the bull's-eye, the inner side of the concentric circular image corresponds to the apex cordis part, and the outer side thereof corresponds to the cardiac base part.
FIG. 3 is a diagram indicating correspondence relationship between myocardial left ventricular short axis MR images and the conventional development representing myocardial blood flow information as shown in FIG. 2.
FIG. 3 shows the relations between MR tomographic images of the myocardium in the left ventricular short axis direction and the small regions in the development image. For example, each small region positioned on the inner side of the development image corresponds to a region divided at the apex cordis part of the myocardium. Each small region positioned in the intermediate part of the development image corresponds to a region divided at the intermediate part of the myocardium. Each small region positioned on the outer side of the development image corresponds to a region divided at the cardiac base part of the myocardium.
FIG. 4 is a diagram showing symptom of subendocardial ischemia schematically by slicing a heart into rings.
In the heart which has developed subendocardial ischemia, blood is not supplied to the inner side of the myocardium, and the medical condition progresses from the inner side toward the outer side of the myocardium. However, the conventional bull's-eye is created by dividing each slice image only radially, and not in the thickness direction of the myocardium. Accordingly, the conventional bull's-eye does not provide precise information with respect to blood flow perfusion that represents the range of ischemia along the myocardial thickness direction.
In particular, magnetic resonance imaging apparatuses generally allow data to be acquired with a high spatial resolution as compared with a method such as a nuclear medicine examination, thereby providing an advantage of depicting a subendocardial ischemia, which has been reported. However, the conventional development image display lacks information with respect to the myocardium along the thickness direction, leading to a problem in that the subendocardial ischemia cannot be evaluated. This is common problem not only for magnetic resonance imaging apparatuses but for any other diagnostic medical imaging apparatuses which are capable of acquiring image data with high spatial resolutions.